1. Field of the Invention:
This invention relates to a catalyst for oxidizing an offensively smelling substance to remove the same from exhaust gas substantially completely and a method of removing any such substance. More particularly, it relates to a catalyst and a method which are particularly effective for removing aldehydes.
2. Description of the Prior Art:
The exhaust gases from the factories and the internal combustion engines of automobiles contain contaminant, explosive, or offensively smelling substances. It is known that those substances can be removed if they are decomposed by oxidation in the presence of a catalyst.
A known catalyst for oxidizing an offensively smelling substance usually comprises a base metal, such as manganese, nickel or chromium, or a noble metal, such as platinum or palladium, or an oxide thereof supported on, for example, an alumina, silica or Kieselguhr carrier. This catalyst is, however, very unsatisfactory for decomposing aldehydes, such as formaldehyde and acetaldehyde, though it is effective for decomposing hydrocarbons, such as toluene and xylene. The exhaust gases usually contain acetaldehyde as a source of an offensive smell. It is one of the worst eight substances specified by the Japanese Law for the Prevention of an Offensive Smell. Its offensive smell is perceivable even if it may exist at a very low concentration. The results of an organoleptic test indicate that its smell does not disappear unless its concentration is reduced to less than 0.01 ppm.
The known catalyst has, however, too low a catalytic activity to oxidize aldehydes completely to remove their offensive smell, though it may be effective for reducing their concentration to some extent.